<!DOCTYPE html>
<html>

<style>
    h1 {
        color: blue;
        text-align: center;
    }

    p {
        color: red;
        text-align: center;
    }

    div {
        background-color: lightgrey;
        width: 300px;
        border: 5px solid green;
        padding: 50px;
        margin: 20px;
    }

    footer {
        background-color: lightgrey;
        width: 300px;
        border: 5px transparent;
        padding: 50px;
        /* margin: 20px; */
    }
</style>

<body>
    <script class="h1">
        var x = 5;
        var y = 6;
        var z = x + y;
        window.alert("This is an alert box!");
        alert(z);
    </script>
    <h1 style="text-align:center;">
        My First Website
    </h1>
    <p style="text-align: end;empty-cells: show;">
        My First Paragraph
    </p>
    <tr>
        <td>Row 1, Column 1</td><br>
        <td>Row 1, Column 2</td>
    </tr>
    <div style="background-color:cornflowerblue">
        <a href="https://cn.bing.com">This is a link to bing.com</a>
        <address>
            Written by
            <a href="mailto: 745727212@qq.com">Goldfish</a>
        </address>
    </div>

    <div style="background-color:aquamarine">
        <footer>
            <p>Posted by: Goldfish</p>
            <p>Contact information:<a href="mailto: 745727212@qq.com">745727212@qq.com</a>
        </footer>
    </div>

</body>

</html>